Anti-reflection films are used in various display devices such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), and a cathode-ray tube (CRT). Further, lenses of glasses or cameras generally have the Anti-reflection films.
As an anti-reflection film, a multi-layered film comprising plural transparent metal oxide layers superposed one on another has been widely employed. The plural transparent metal oxide layers lower reflections of light in a wide wavelength region. The layers are formed by chemical vapor deposition (CVD) process or physical vapor deposition (PVD) process (especially, vacuum deposition process).
On a support having a rough surface of anti-glare coating, an anti-reflection film is often formed by PVD process. This film reduces the transmittance of parallel rays as compared with a film provided on a smooth support. In spite of that, since the roughness on the support scatters light to prevent the film from reflecting the surrounding scene, a device equipped with that film can display a remarkably improved image.
Although the transparent metal oxide layers thus give an anti-reflection film having the excellent optical characteristics, the deposition process has insufficient productivity for mass-production.
In place of the deposition process, it is proposed to apply a coating liquid containing inorganic fine particles to prepare an anti-reflection film.
Japanese Patent Publication No. 60(1985)-59250 describes an anti-reflection film comprising fine holes and inorganic fine particles. The film is formed by applying a coating liquid, and the formed film is subjected to active gas treatment. Through the treatment, the gas escapes from the film to form the fine holes.
Japanese Patent Provisional Publication No. 59(1984)-50401 describes an anti-reflection film comprising a support, a high refractive index layer and a low refractive index layer superposed in this order. The publication also discloses an anti-reflection film further comprising a middle refractive index layer provided between the support and the high refractive index layer. In each film, the low refractive index layer is formed by applying a coating liquid containing a polymer or inorganic fine particles.
Japanese Patent Provisional Publication No. 2(1990)-245702 discloses an anti-reflection film comprising two or more kinds of micro particles (for example, SiO2 and MgF2). The mixing ratio of the particles varies in the thickness direction so that the refractive index may gradually vary along the thickness. The film having that structure has optical characteristics similar to those of the film in No. 59(1984)-50401, which comprises both high and low refractive index layers. In the film of No. 2(1990)-245702, the micro particles are combined with SiO2 formed by thermal decomposition of ethyl silicate. In the thermal decomposition, the ethyl part of ethyl silicate is burnt to evolve carbon dioxide and water vapor. The produced carbon dioxide and water vapor escape from the film to form voids among the micro particles (as shown in FIG. 1 of the Publication).
Japanese Patent Provisional Publication No. 5(1993)-13021 discloses an anti-reflection film in which the voids described in No. 2(1990)-245702 are filled with a binder.
Japanese Patent Provisional Publication No. 7(1995)-48527 discloses an anti-reflection film containing a binder and inorganic fine particles of porous silica.
In order to reduce glare of a wet-type anti-reflection film, the above-described process in which the film is formed on a rough support and the process in which matting particles are added into the coating liquid were thus developed and proposed. However, in the former process, the coating liquid applied on convex parts of the rough surface flows into concave parts to form a layer having an uneven thickness. Consequently, the resulting film poorly reduces reflection as compared with a film formed on a smooth surface. On the other hand, in the latter, it is needed to incorporate the matting particles having sizes of about 1 μm or more into a thin film having a thickness of 0.1 to 0.3 μm, and accordingly the particles are apt to defect from the film. Therefore, an anti-reflection film having both sufficient film strength and satisfying anti-glare performance had been hardly produced by applying a coating liquid.